1. Field of the Invention
The invention relates to an optical projecting system, more particularly to an optical projecting system capable of reducing losses in light energy.
2. Description of the Related Art
As shown in FIG. 1, a conventional optical projecting system includes a light source 1, a light tunnel 2, a transmissive color wheel 3, a digital micro-mirror device (DMD) 4, and a screen 5. The light source 1 is capable of providing source light 101. The light tunnel 2 is capable of receiving, guiding, and focusing the source light 101 to result in focused light. The transmissive color wheel 3 is rotatable about a rotation axis (X1), and includes a plurality of spiral light-filtering components 301 that are distributed around the rotation axis (X1). The light-filtering components 301 of the transmissive color wheel 3 include sequentially arranged red, blue and green light-filtering components (r), (b), (g), as best illustrated in FIG. 2. The red, blue and green light-filtering components (r), (b), (g) allow transmission of red, blue and green light therethrough, respectively. The transmissive color wheel 3 rotates at an extremely high speed about the rotation axis (X1) as the focused light exits the light tunnel 2 so as to filter the focused light into red, blue and green focused light components sequentially and cyclically. The red, blue and green focused light components are subsequently projected toward the DMD 4, which then modulates the red, blue and green focused light components into red, blue and green modulated light components, respectively, and projects them onto the screen 5 so that colored images are presented on the screen 5.
Although the conventional optical projecting system is capable of projecting colored images, the following shortcomings exist during use:
1. As shown in FIG. 2, when the focused light passes through the red light-filtering component (r), only the red focused light component thereof is transmitted toward the DMD 4, while the blue and green focused light components are reflected back to the light tunnel 2. Similarly, when the focused light passes through the blue light-filtering component (b), only the blue focused light component thereof is transmitted toward the DMD 4, while the red and green focused light components are reflected back to the light tunnel 2. When the focused light passes through the green light-filtering component (g), only the green focused light component thereof is transmitted toward the DMD 4, while the red and blue focused light components are reflected back to the light tunnel 2. This results in high losses in light energy, i.e., reduction in light utilization, in addition to presenting adverse effects on brightness of projected images.
2. Although a small portion of the focused light components that are reflected back to the light tunnel 2 by the red, blue and green light-filtering components (r), (b), (g) can eventually reach the transmissive color wheel 3, the focused light components that are reflected back to the light tunnel 2 can cause the light tunnel 2 to overheat such that the service life of the light tunnel 2 is shortened and the quality of the conventional optical projecting system is thus adversely affected.
3. As shown in FIG. 1, the light source 1, the light tunnel 2, the transmissive color wheel 3, and the DMD 4 are aligned along the rotation axis (X1). In addition, the light tunnel 2 extends along the rotation axis (X1) and has a definite length. For these reasons, the conventional optical projecting system is bulky and occupies too much space.
As shown in FIG. 3, another transmissive color wheel 6 is used instead of the transmissive color wheel 3 in a modified conventional optical projecting system. The transmissive color wheel 6 includes three fan-shaped light-filtering components 601, which include red, blue, and green light-filtering components (r′), (b′), (g′) that allow transmission of red, blue, and green light therethrough, respectively. Therefore, as with the red, blue and green light-filtering components (r), (b), (g) of the transmissive color wheel 3, the red, blue, and green light-filtering components (r′), (b′), (g′) of the transmissive color wheel 6 only allow corresponding colors of the focused source light 101 to be transmitted therethrough, with a major portion of the focused source light 101 reflected back to the light tunnel 2 (as shown in FIG. 1).